Apparatus and method for adaptive I/Q imbalance compensation

• US 8,509,298 B2
• Filed: 01/06/2011
• Issued: 08/13/2013
• Est. Priority Date: 01/06/2011
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Hormis, Raju
• Primary Examiner(s): Nguyen, Lee
• Application Number:
  US12/986,093
• Publication Number:
  US 20120178392A1
• Time in Patent Office: 950 Days
• Field of Search: 375/232, 375/235, 375/261, 375/279, 375/284, 375/285, 375/329, 375/350, 455/285, 455/296, 455/302
• US Class Current: 375/232
• CPC Class Codes: H03D 3/009 Compensating quadrature phase or amplitude imbalances
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

An I/Q imbalance compensation block of a RF receiver for compensating an imbalance between an in-phase component and a quadrature component of an RF signal is disclosed. The compensation block includes a conjugation block; an adaptive finite impulse response (FIR) filter; and an adder. The filter use filter coefficients iteratively updated at least partly in response to a compensated digital signal. The filter can have a complex number for at least one, but not all of filter taps, and real numbers for other filter taps. The filter can be provided with adaptation step sizes different from filter tap to filter tap. The filter can also be provided with an adaptation step size(s) varying over time. The filter can also be provided with an adaptation step size(s) divided by the square norm of the compensated signal.

Claims

1. An apparatus comprising:

a finite impulse response (FIR) filter configured to filter a version of a digital signal to generate a compensation signal, wherein the FIR filter has filter coefficients, wherein the digital signal comprises a digital representation of a demodulated in-phase and quadrature phase component of a radio frequency (RF) signal;

an adder configured to sum another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal; and

an adaptation step size adaptor configured to provide two or more different adaptation step sizes for updating the filter coefficients, wherein a selected one of the two or more different adaptation step sizes is configured to be multiplied with two or more samples of the balanced digital signal to generate an adjustment for a filter coefficient of the FIR filter,

wherein one of the versions of the digital signal or the version of the compensation signal is a complex conjugate of the digital signal or a complex conjugate of the compensation signal, respectively, and the others are not the complex conjugates, wherein the FIR filter and the adder comprise electronic hardware.

2. The apparatus of claim 1, further comprising:

a delay element configured to delay the balanced digital signal; and

a filter adaptation block configured to generate a feedback signal using the delayed balanced digital signal, and to provide the feedback signal to the FIR filter through the adaptation step size adaptor for updating the filter coefficients.

3. The apparatus of claim 1, wherein the adaptation step size adaptor is further configured to vary adaptation step sizes for one or more of the filter coefficients over time.

4. The apparatus of claim 3, wherein the FIR filter has X real number filter coefficients and Y imaginary number coefficients, wherein Y is less than X.

5. The apparatus of claim 3, wherein the adaptation step size adaptor is further configured to divide adaptation step sizes for one or more of the filter coefficients by a squared norm of the balanced digital signal.

6. The apparatus of claim 5, wherein the FIR filter has X real number filter coefficients and Y imaginary number coefficients, wherein Y is less than X.

7. The apparatus of claim 6, wherein the FIR filter has only 1 imaginary number coefficient and the 1 imaginary number coefficient is present only for a first tap of the FIR filter.

8. The apparatus of claim 1, wherein the adaptation step size adaptor is further configured to divide adaptation step sizes for one or more of the filter coefficients by a squared norm of the balanced digital signal.

9. The apparatus of claim 8, wherein the FIR filter has X real number filter coefficients and Y imaginary number coefficients, wherein Y is less than X.

10. An apparatus comprising:

a finite impulse response (FIR) filter configured to filter a version of a digital signal to generate a compensation signal, wherein the FIR filter has filter coefficients, wherein the digital signal comprises a digital representation of a demodulated in-phase and quadrature phase component of a radio frequency (RF) signal;

an adder configured to sum another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal; and

an adaptation step size adaptor configured to vary adaptation step sizes over time for adaptive adjustment of one or more of the filter coefficients such that the one or more filter coefficients are updated based at least partly on a multiplication product of a selected one of a plurality of different step sizes and two or more samples of the balanced digital signal,

wherein one of the versions of the digital signal or the version of the compensation signal is a complex conjugate of the digital signal or a complex conjugate of the compensation signal, respectively, and the others are not the complex conjugates, wherein the FIR filter and the adder comprise electronic hardware.

11. The apparatus of claim 10, further comprising:

a delay element configured to delay the balanced digital signal;

a filter adaptation block configured to generate a feedback signal using the delayed balanced digital signal, and to provide the feedback signal to the FIR filter through the adaptation step size adaptor for updating the filter coefficients.

12. The apparatus of claim 10, wherein the adaptation step size adaptor is further configured to divide adaptation step sizes for one or more of the filter coefficients by a squared norm of the balanced digital signal.

13. The apparatus of claim 12, wherein the FIR filter has X real number filter coefficients and Y imaginary number coefficients, wherein Y is less than X.

14. An apparatus comprising:

a finite impulse response (FIR) filter configured to filter a version of a digital signal to generate a compensation signal, wherein the FIR filter has filter coefficients, wherein the digital signal comprises a digital representation of a demodulated in-phase and quadrature phase component of a radio frequency (RF) signal;

an adder configured to sum another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal; and

an adaptation step size adaptor configured to provide adaptation step sizes for updating the filter coefficients, wherein the adaptation step size adaptor is configured to divide adaptation step sizes for one or more of the filter coefficients by a squared norm of the balanced digital signal,

wherein one of the versions of the digital signal or the version of the compensation signal is a complex conjugate of the digital signal or a complex conjugate of the compensation signal, respectively, and the others are not the complex conjugates, wherein the FIR filter and the adder comprise electronic hardware.

15. A method of improving an image rejection ratio of a digital signal having demodulated in-phase and quadrature-phase components of a radio frequency signal, the method comprising:

filtering a version of the digital signal with a finite impulse response (FIR) filter having filter coefficients to generate a compensation signal, wherein filtering is implemented by hardware or by instructions implemented by a processor;

generating a complex conjugate of the digital signal or the compensation signal;

summing another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal, wherein one of the versions of the digital signal and the version of the compensation signal corresponds to a complex conjugate of the digital signal or the compensation signal, respectively, and the others are not the complex conjugates;

generating a feedback signal by multiplying a correlation of the balanced digital signal with two or more different adaptation step sizes to generate adjustments for the filter coefficients; and

determining the filter coefficients, using the feedback signal.

16. The method of claim 15, wherein generating the feedback signal further comprises varying at least one of the adaptation step sizes over time.

17. The method of claim 15, wherein generating the feedback signal further comprises dividing at least one of the adaptation step sizes by a squared norm of the balanced digital signal.

18. A method of improving an image rejection ratio of a digital signal having demodulated in-phase and quadrature-phase components of a radio frequency signal, the method comprising:

filtering a version of the digital signal with a finite impulse response (FIR) filter having filter coefficients to generate a compensation signal, wherein filtering is implemented by hardware or by instructions implemented by a processor;

generating a complex conjugate of the digital signal or the compensation signal;

summing another version of the digital signal and a version of the compensation signal to a generate a balanced digital signal that has an improved image rejection ratio versus the digital signal, wherein one of the versions of the digital signal and the version of the compensation signal corresponds to a complex conjugate of the digital signal or the compensation signal, respectively, and the others are not the complex conjugates;

generating a feedback signal by multiplying a correlation of the balanced digital signal with one or more adaptation step sizes to generate adjustments for the filter coefficients, wherein at least one of the adaptation step sizes is varied over time; and

determining the filter coefficients, using the feedback signal.

19. The method of claim 18, wherein generating the feedback signal further comprises dividing at least one of the adaptation step sizes by a squared norm of the balanced digital signal.

20. A method of improving an image rejection ratio of a digital signal having demodulated in-phase and quadrature-phase components of a radio frequency signal, the method comprising:

filtering a version of the digital signal with a finite impulse response (FIR) filter having filter coefficients to generate a compensation signal, wherein filtering is implemented by hardware or by instructions implemented by a processor;

generating a complex conjugate of the digital signal or the compensation signal;

summing another version of the digital signal and a version of the compensation signal to generate a balanced digital signal that has an improved image rejection ratio versus the digital signal, wherein one of the versions of the digital signal and the version of the compensation signal corresponds to a complex conjugate of the digital signal or the compensation signal, respectively, and the others are not the complex conjugates;

generating a feedback signal by multiplying a correlation of the balanced digital signal with one or more adaptation step sizes for the filter coefficients, wherein the one or more of the adaptation step sizes is divided by a squared norm of the balanced digital signal; and

determining the filter coefficients, using the feedback signal.